By Ali Vitali with NBC News Politics&bullet;
last updated:
21/12/2018

Defense Secretary Jim Mattis' impending departure shook an already tense Capitol on Thursday night, with lawmakers in both parties reacting with concern over what Mattis' departure means for both Trump's administration, and the international community.

In a letter announcing his resignation, Mattis implicitly criticized President Donald Trump's military judgment, suggested the president was not treating allies with respect, and had not been "clear-eyed" about those who would do the U.S. harm.

He then told Trump that he had the right to have a defense chief who shares his views.

Sen. Mark Warner, D-Va., the top Democrat on the Senate Intelligence Committee, called Mattis "an island of stability amidst the chaos of the Trump administration." Mattis, in his letter, said he would depart at the end of February.

"This is scary," Warner tweeted.

Sen. Chris Murphy, D-Conn., called it a "national security crisis."

"A Secretary of Defense quitting over a public disagreement with a President whose foreign policy he believes has gone off the rails is a national security crisis," Murphy tweeted, surmising a "morale crisis at the Department of Defense right now" after the news of Mattis' impending departure and Trump's decision to withdraw U.S. troops from Syria, announced just a day earlier.

Republicans were also unbridled in voicing their concern Thursday night. Republican Rep. Adam Kinzinger R-Ill., quote-tweetingthe president's announcement about Mattis, said: "That's what happens when you ignore sound military advice."

"This is a sad day for America because Secretary Mattis was giving advice the President needs to hear," Nebraska Republican Sen. Ben Sasse said in a statement.

Trump first announced the news of Mattis' departure on Twitter, portraying it as a retirement. Sen. Marco Rubio, R-Fla., attempted an optimisticview, saying he hoped the general's "decision to resign was motivated solely by a desire to enjoy a well deserved retirement."

That sentiment was quickly replaced, however, after Rubio read Mattis' letter — which did not include any praises or compliments of the president and implicitly criticized the president's military judgment.

To Rubio, the letter "makes it abundantly clear that we are headed towards a series of grave policy errors which will endanger our nation,damage our alliances & empower our adversaries." He also pressed for more oversight of the executive branch by Congress.

Senator Lindsey Graham, R-S.C., had praised Mattis earlier in the day, noting disagreement between the president and the Pentagon chief over Trump's recently announced decision to withdraw U.S. troops from Syria. Though one of Trump's staunchest defenders, Graham has been vocal in his opposition to the move.

Mattis "thought that it was not the time was not right to leave [Syria], for all the reasons just expressed. Secretary Mattis is one of the most seasoned national security people I know, he's got a great team around him, the President does, he just has to listen," Graham said in a news conference.

Thursday night, Graham tweeted: "It is with great sadness that I was informed of the resignation of General Mattis."